Three-phase generators are normally used for the supply of electrical voltage or current for the consumers of a motor vehicle. Such three-phase generators are designed to have three or more phases. For the generation of the needed direct voltage or the needed direct current, the generators or three-phase generators used include rectifiers having rectifying elements which in a three-phase generator are normally made up of six silicon pn diodes. Normally the diodes are packaged in a press-fit housing and pressed into openings of the rectifier provided for this purpose. Such press-fit diodes are discussed, for example, in DE-195 49 202 A.
Conventional rectifiers having diodes of the above-mentioned design have forward power losses caused by the unavoidable forward voltages of the pn diodes. This is accompanied by a deterioration of the efficiency of the generator. Since on average two diodes are always connected in series, the mean forward power losses in a 100 ampere generator are approximately 200 watts. The heating of the diodes or of the rectifier caused by these losses must be reduced by complex cooling measures, for example a suitable heat sink and an associated fan.
A significant reduction of the voltage loss and accordingly an enhancement of the efficiency of a generator are able to be achieved by using power field effect transistors instead of diodes. In order to function as rectifiers, such power field effect transistors must be actively triggered. Such an active rectification is substantially more complex than a simple diode rectification in conventional rectifiers, since additional triggering electronics are needed for active rectification. In this connection, the thermal-mechanical design of the generator must be completely reconfigured for the use of power field effect transistors compared to conventional generators.